Key takeaways

Tamiflu (oseltamivir phosphate) is used to treat or prevent the flu in adults and children.
Common side effects include nausea, vomiting, headache, and more severe but rare side effects such as abnormal behavior and severe allergic reactions.
Side effects of Tamiflu are usually temporary, with most disappearing a few days after treatment starts; however, severe allergic reactions require immediate medical attention.
To minimize side effects, Tamiflu should be taken as directed, preferably with food to reduce gastrointestinal discomfort, and patients should be monitored for any changes in behavior or signs of allergic reaction.

Tamiflu is a brand name prescription drug that treats active influenza A and B infections in people 2 weeks or older. It is also used to help prevent flu infections in people 1 year and older during flu season. The active ingredient in Tamiflu, oseltamivir phosphate, prevents the flu virus from infecting healthy cells and producing new influenza virus particles.

Tamiflu generally has more moderate side effects and fewer drug interactions than other antiviral medications, but some people may experience problems while taking it. Even though Tamiflu is often used in emergencies, it helps to be aware of these possible problems and tips to avoid them while taking it in a non-emergency setting.

RELATED: What is Tamiflu?

Common side effects of Tamiflu

Most people taking Tamiflu will not experience side effects. For those who do, unwanted side effects will be moderate and temporary, largely gastrointestinal problems such as nausea and vomiting. The most common Tamiflu side effects are:

Nausea
Vomiting
Headache
Stomach pain
Nosebleeds
Fatigue
Diaper rash (in infants ranging in age from premature babies to 36 weeks)

If flu symptoms get worse while taking Tamiflu, contact a healthcare professional for medical advice.

Serious side effects of Tamiflu

Serious side effects were not reported during clinical trials, but have been reported in the later use of the drug. These include:

Abnormal behavior
Delirium
Self-injury
Exacerbation of irregular heartbeat (arrhythmia)
Anaphylaxis (a severe allergic reaction that includes trouble breathing and a dangerous drop in blood pressure)
Severe allergic skin reactions including erythema multiforme, Stevens-Johnson syndrome, and toxic epidermal necrolysis

Tamiflu and neuropsychiatric disorders

Tamiflu treatment has been associated with neurological and psychiatric adverse effects when used to prevent flu infection, particularly in children. Statistically, people taking Tamiflu are 1% more likely to experience these psychiatric side effects, including delusions (wrong beliefs about reality), hallucinations (hearing or seeing things that aren’t there), delirium, abnormal behaviors, and self-harm, which can sometimes be fatal. Neurological symptoms include headache, convulsions, and shakiness.

These psychotic and behavioral side effects usually appear early and suddenly when taking Tamiflu and are typically short-lived, often going away rapidly. Caregivers should carefully watch anyone taking Tamiflu for any changes in mental status, such as confusion, hallucinations, delusions, or odd behaviors, and immediately contact a healthcare provider if they are present.

Tamiflu and vomiting

Although Tamiflu has few side effects, the most commonly experienced ones are nausea and vomiting. In clinical trials, 10% of people taking Tamiflu experienced nausea compared to 6% in the placebo group and 8% experienced vomiting compared to 4% in the placebo group. Among children, up to 16% reported vomiting as a side effect.

In most people taking Tamiflu, nausea and vomiting are not severe and typically start in the first two days of treatment. Taking Tamiflu with food or milk may decrease the likelihood or severity of these side effects.

How long do Tamiflu side effects last

Most people take Tamiflu for only a few days and will experience no or only moderate side effects. Most temporary side effects, including headache, nausea, vomiting, and psychiatric disturbances, appear early and often improve a few days after starting treatment. Some side effects, such as diaper rash in infants, may be delayed and take a few days to get better.

Severe allergic reactions, such as anaphylaxis, can have a very sudden onset, but severe skin reactions typically are delayed. Any severe allergic reaction could be life-threatening and may take a few days of emergency medical care to fully resolve.

Tamiflu contraindications & warnings

Although Tamiflu generally has mild side effects and very few drug interactions, it still may not be right for everyone. Some people may not be able to take this medication at all, but others may need to take it cautiously and with extra monitoring.

Abuse and dependence

Tamiflu is not a drug that is used recreationally or that causes physical dependence. Typically, Tamiflu is only prescribed for five to 10 days, enough time for flu symptoms to get better. In some cases, however, Tamiflu can be given for six to 12 weeks to prevent flu transmission in vulnerable populations during a community outbreak or flu pandemic. No matter how long Tamiflu is taken, discontinuing treatment does not cause withdrawal symptoms or other adverse events.

Overdose

No side effects have been reported in the majority of people who have taken a Tamiflu overdose, but some people have experienced normal side effects when taking too high of a dose. As with any prescription drug, get immediate medical help if there’s any suspicion of a Tamiflu overdose.

Contraindications

Tamiflu should never be used in patients with a known serious allergy to oseltamivir or any of the inactive ingredients in the drug.

Restrictions

Other medical conditions may require caution, extra care, or monitoring when Tamiflu is administered.

Fructose intolerance: Because Tamiflu oral suspension contains sorbitol, people with serious hereditary fructose intolerance should only be given Tamiflu capsules. A standard dose of Tamiflu oral suspension (75 mg) contains 2 grams of sorbitol, exceeding the daily limit for those with hereditary fructose intolerance. People with mild fructose intolerance may experience side effects such as nausea, vomiting, abdominal pain, and diarrhea.
Kidney problems: People with moderate to severe renal impairment will be given lower doses of Tamiflu to lower the risk of side effects. Healthcare professionals are advised not to prescribe Tamiflu to anyone with end-stage renal disease unless they are undergoing dialysis.

Pregnancy and nursing

Although Tamiflu has been shown to cause fetal problems in animals, it has not been fully studied in pregnant women. It is not certain if it is safe to take while pregnant. It is known, however, that a flu infection can cause problems such as low birth rate, premature birth, birth defects, and even the death of the baby. Pregnant women should discuss the risks and benefits of taking Tamiflu with a healthcare provider.

The Centers for Disease Control and Prevention (CDC) strongly urge all women who are pregnant or planning to become pregnant to get a flu shot to prevent flu infections rather than rely on antiviral drugs such as oseltamivir.

Oseltamivir may be present in breast milk, but the amount is believed to be far below the normal dose that would be given to an infant. So far there is no evidence of any harm to a breastfeeding baby. Both the mother and her healthcare provider will need to make a decision balancing the benefits of taking Tamiflu against any possible risks to the infant.

Children

The Food and Drug Administration (FDA) has approved oseltamivir to treat flu infections in children as young as 2 weeks old who are at a high risk for complications. It is also FDA-approved to prevent flu infections in high-risk children as young as 1 year old. Its pediatric use in younger children has not been established as safe or effective.

Seniors

Tamiflu has been shown to be as safe and effective in people older than the age of 65 years as it is in younger adults.

Tamiflu interactions

Tamiflu has very few drug interactions that cause problems.

Live flu vaccines should not be given two weeks before or 48 hours after oseltamivir treatment.
Drugs such as clopidogrel may reduce the effectiveness of Tamiflu therapy. For people taking clopidogrel, a drug that prevents blood clots, alternative blood thinners should be used.
Drugs such as probenecid and dichlorphenamide block the body’s ability to break down oseltamivir, increasing the risk of side effects.
How to avoid Tamiflu side effects

Most people taking Tamiflu will experience no or moderate side effects. Even so, side effects and drug interactions are possible, so a few helpful tips can help prevent or minimize problems.

1. Tell the doctor about all medical conditions and medications

The first place to start in avoiding side effects is to tell the healthcare provider prescribing Tamiflu about all past and present medical conditions, especially:

Kidney problems
Heart problems
Breathing problems or chronic lung disease
Fructose intolerance
Any condition that causes swelling or disorder of the brain
Weakened immune system
Pregnancy or plans to become pregnant
Breastfeeding or plans to breastfeed

Some side effects may be caused by accidental drug interactions, but these are very rare. Still, healthcare professionals should be given a patient’s complete list of all prescriptions, over-the-counter medications, and dietary supplements being taken before any prescription is written. In particular, a healthcare provider should be made aware of any live attenuated influenza vaccine that has been given in the last two weeks because it could delay Tamiflu treatment in some cases.

2. Ask for a flu test

Tamiflu will provide no benefit for any infection or problem other than an influenza infection. Make sure the healthcare provider prescribing Tamiflu administers a flu test to verify the infection.

3. Take Tamiflu as directed

Take Tamiflu as prescribed. Read the medication guide carefully and follow the instructions on how to take a dose. The usual dose is 75 mg taken twice a day for five to seven days. Don’t skip a dose or take extra medicine.

4. Take Tamiflu with food

Tamiflu can be taken with a meal or on an empty stomach. To avoid nausea, vomiting, and other gastrointestinal side effects, take Tamiflu with food or milk.

5. Watch for behavior changes

Though rare, Tamiflu can cause changes in mental status or behavior, particularly in children. In some cases, these side effects can be fatal. Watch closely for changes such as:

Confusion
Hallucinations (hearing voices or seeing things that aren’t there)
Strange beliefs
Unusual behaviors
Shakiness
Convulsions

Most of these problems will appear in the first couple of days after the initiation of Tamiflu treatment. Contact a healthcare provider immediately if they do.

6. Watch for signs of an allergic reaction

Tamiflu can cause allergic reactions. Most, including both mild and severe allergic reactions, will affect the skin, but an anaphylactic reaction is possible, too. Watch for signs of an allergic reaction such as:

Skin rash
Itching
Hives
Blisters
Peeling
Swelling of the face, mouth, lips, or throat
Trouble breathing
Chest pain

If any signs of an allergic reaction are noticed, get immediate emergency medical help. Tamiflu will need to be discontinued.

Resources:

Oseltamivir, StatPearls.
Tamiflu, Epocrates.
Tamiflu: Consumer questions and answers, Food and Drug Administration (FDA)
Tamiflu drug summary, Prescriber’s Digital Reference
Tamiflu label changed to warn of self-harm, PharmaTimes
Tamiflu website, Genentech/Roche